Optical isolator

ABSTRACT

An optical isolator capable of simultaneously transmitting a plurality of light beams emitted from a plurality of optical fibers in one direction. It includes a plurality of optical fibers for transmitting light beams; a pair of collimating lenses for converting the light beams, emitted from or entered into the optical fibers, into parallel light beams; a pair of symmetric birefringent elements having at least one tapered surface for emitting by polarization the plurality of parallel light beams having passed the collimating lenses, and condensing all the light beams traveling in a forward direction onto the optical fibers, respectively; and a Faraday rotator interposed between the birefringent elements for rotating the light beams incident thereto by 45 degrees. A plurality of tapered faces having the same tapered angle are formed on one surface of the birefringent element so that a plurality of light beams can be simultaneously transmitted in one direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to an optical transmissionsystem for transmitting prescribed information utilizing light. Inparticular, the present invention relates to an optical isolator whichtransmits light in one direction without loss, but intercepts the lighttransmission in the opposite direction.

2. Description of the Prior Art

Nowadays, as the social activities become diverse and complicated, theamount of information communicated by human-to-human, human-to-computer,computer-to-machine, etc., has been gradually increased.

Accordingly, various techniques for transmitting the diverse andlarge-scaled information accurately, rapidly, and distantly have beensteadily developed. As one among such developed techniques, an opticaltransmission system has been commercialized, and this brings thenecessity for optical devices having more diverse functions.

One of such optical devices for use in the optical transmission systemis an optical isolator. To protect a light source, for instance, such aslaser diodes, the optical isolator passes the light in a forwarddirection, but intercept the light transmitted in a backward direction.

FIGS. 1 and 2 illustrate the structure of a conventional opticalisolator which is disclosed in U.S. Pat. No. 4,548,478.

This conventional optical isolator includes a Faraday rotator 4 forrotating by 45° the light incident through an optical path between firstand second optical fibers 1 and 7, and first and second birefringentelements 3 and 5 placed in front and rear of the Faraday rotator 4,respectively.

Each of the first and second birefringent elements 3 and 5 has a taperedsurface with a predetermined tapered angle θ, and the optical axesthereof cross each other with an angle of 45°.

The optical isolator also includes first and second collimating lenses 2and 6 for converting the light emitted from the first and second opticalfibers 1 and 7 into parallel light beams.

According to the conventional optical isolator, as shown in FIG. 1, inthe event that the light travels in a forward direction, i.e., from thefirst birefringent element 3 to the second birefringent element 5, thelight emitted from the first optical fiber 1 is converted into parallellight beams, by passing through the first collimating lens 2.

The parallel light beams transmitted from the first collimating lens 2is entered into the first birefringent element 3, and then divided intoordinary rays o and extraordinary rays e. These ordinary andextraordinary rays o and e are rotated by 45° by the Faraday rotator 4.

Thereafter, the ordinary and extraordinary rays o and e, which have beenrotated by 45°, pass through the second birefringent element 5 to berefracted and converted into parallel light beams. This parallel lightbeams are condensed through the second collimating lens 6, and thenentered into the second optical fiber 7.

Meanwhile, as shown in FIG. 2, in the event that the light travels in abackward direction, i.e., from the second birefringent element 5 to thefirst birefringent element 3, the parallel light beams transmitted fromthe second collimating lens 6 are entered into the second birefringentelement 5, and then divided into the ordinary rays o and theextraordinary rays e. These ordinary and extraordinary rays o and e arerotated clockwise by the Faraday rotator 4.

At this time, since the optical axes of the first and secondbirefringent elements 3 and 5 cross each other, the direction of theordinary rays o make a right angle with that of the extraordinary rayse, and this causes the ordinary and the extraordinary rays o and eincident to the first birefringent element 3 to be reversed from eachother.

Accordingly, the reversed light rays o_(e) and e_(o) having passedthrough the first birefringent element 3 cannot become parallel beams,but respectively pass through the first collimating lens 2 with anglespredetermined in accordance with the tapered angle θ of the first andsecond birefringent elements 3 and 5. Accordingly, the reversed lightrays travel in left and right directions, or upper and lower directionsof the first optical fiber 1, and thus cannot be entered into the coreof the first optical fiber 1.

As a result, if the light travels in the backward direction of theoptical isolator, a great loss of light is produced, and thus the lighttransmission is intercepted.

However, according to the conventional optical isolator, since the firstand second birefringent elements 3 and 5 have only one tapered surface,only one optical signal can be propagated through the optical fibers 1and 7, resulting in that only one optical signal can be transmitted byone optical isolator.

Accordingly, in the wavelength division multiplexing communicationfields utilizing a plurality of optical signals, a plurality of opticalisolators should be employed to simultaneously transmit the opticalsignals, and this causes the size of the optical system and themanufacturing cost thereof to be increased.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an optical isolatorwhich can transmit a plurality of light beams emitted from a pluralityof optical fibers in one direction.

In order to achieve the above object, there is provided an opticalisolator comprising:

a plurality of optical fibers for transmitting light beams;

a pair of collimating lenses for converting the light beams emitted fromor entered into the optical fibers into parallel light beams;

a pair of symmetric birefringent elements, having at least one taperedsurface, for emitting by polarization the plurality of parallel lightbeams having passed the collimating lenses and condensing all the lightbeams traveling in a forward direction onto the optical fibers,respectively; and

a Faraday rotator, interposed between the birefringent elements, forrotating the light beams incident thereto by 45°.

BRIEF DESCRIPTION OF THE DRAWINGS

The above object, other features, and advantages of the presentinvention will become more apparent by describing the preferredembodiment thereof with reference to the accompanying drawings, inwhich:

FIG. 1 is a schematic view illustrating the optical path of aconventional optical isolator in case that the light travels in aforward direction.

FIG. 2 is a schematic view illustrating the optical path of aconventional optical isolator in case that the light travels in abackward direction.

FIG. 3 is a schematic view illustrating the optical path of the opticalisolator according to the present invention in case that the lighttravels in a forward direction.

FIG. 4 is a schematic view illustrating the optical path of the opticalisolator according to the present invention in case that the lighttravels in a backward direction.

FIGS. 5A to 5C are front, left side, and right side views of the doublerefracting element of FIG. 3, respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiment of the present invention will be explained indetail with reference to FIGS. 3, 4, 5A to 5C.

FIGS. 3 and 4 show the structure of the optical isolator according tothe present invention. In detail, FIG. 3 is a schematic viewillustrating the optical path of the optical isolator in case that thelight travels in a forward direction, and FIG. 4 is a schematic viewillustrating the optical path of the optical isolator in case that thelight travels in a backward direction.

In the present invention, description of the same structure as theconventional optical isolator as described above will be omitted.

Referring to FIGS. 3 and 4, the present invention is directed to aso-called multi-isolator which transmits optical signals emitted from aplurality of optical fibers 12 and 14 provided at one side of theisolator to a plurality of optical fibers 72 and 74 provided at theother side of the isolator without loss, but intercepts the transmissionof the optical signals in the opposite direction.

A Faraday rotator 40 is interposed between first and second birefringentelements 30 and 50.

Each of the first and second birefringent elements 30 and 50, as shownin FIGS. 5A to 5C, has a pair of tapered faces 32 and 34, or 52 and 54which are symmetrically formed on one surface thereof based on ahorizontal dividing line and which have a predetermined tapered angle φ.

Especially, the first and second birefringent elements 30 and 50 are soarranged that the tapered faces 32, 34, 52, and 54 thereof face thefirst and second collimating lenses 20 and 60, respectively.

Also, the crystal axis of the first or second collimating lens 20 or 60has an angle of 45° clockwise or counter clockwise.

The operation of the optical isolator including the first and secondbirefringent elements 30 and 50 according to the present invention willnow be explained.

First, in the event that light beams propagate in the forward directionas shown in FIG. 3, the light beams emitted from the optical fibers I2and 14 are converted into parallel light beams by passing through thefirst collimating lens 20, and the parallel light beams are entered ontothe tapered faces 32 and 34 of the first birefringent element 30 whichhave the same tapered angle φ.

The parallel light beams incident to the first birefringent element 30are divided into ordinary rays O and extraordinary rays E bypolarization. The polarized ordinary and extraordinary rays are enteredinto the Faraday rotator 40 to be rotated clockwise or counterclockwisein accordance with the magnetic polarity of the Faraday rotator 40.

The ordinary rays O and the extraordinary rays E are entered into thesecond birefringent element 50, and refracted from the tapered faces 52and 54 to be converted into parallel light beams. These parallel lightbeams are kept as the ordinary rays O and the extraordinary rays Ethrough the second collimating lens 60, and then condensed into theoptical fibers 72 and 74 as they are.

In other words, the second birefringent element 50 has been rotated by45° in the same direction as the rotating direction of light relative tothe first birefringent element 30).

Accordingly, the ordinary rays O pass through the first and secondbirefringent elements 30 and 50, and then are outputted as they stand,while the extraordinary rays E pass through the first and secondbirefringent elements 30 and 50, and then are outputted as they stand.

On the contrary, in the event that light beams propagate in the backwarddirection as shown in FIG. 4, the light beams emitted from the opticalfibers 72 and 74 are converted into parallel light beams by the secondcollimating lens 60, and then the parallel light beams are entered intothe tapered faces 52 and 54 of the second birefringent element 50 whichhave the same tapered angle φ.

The parallel light beams are polarized and divided into ordinary rays Oand extraordinary rays E through the second birefringent element 50, andthen the polarized ordinary and extraordinary rays are rotated by 45° inthe direction opposite to the rotating direction of the Faraday rotator40.

The ordinary rays O and the extraordinary rays E from the Faradayrotator 40, however, cannot be converted into parallel light beams fromthe tapered faces 32 and 34 of the first birefringent element 30, butemanate from the tapered faces 32 and 34 as divergent light rays.

Specifically, the ordinary rays O become the extraordinary rays E_(o)and the extraordinary rays E become the ordinary rays O_(e), so thatthey are condensed into left and right sides, or upper and lower sidesof the optical fibers 12 and 14 after passing through the firstcollimating lens 20.

As a result, if the light beams propagate in the backward direction,they cannot be entered into the cores of the optical fibers 12 and 14.

As described above, according to the present invention, since aplurality of optical or wavelength signals can be simultaneouslytransmitted in one direction using birefringent elements having aplurality of tapered faces of the same tapered angle, the manufacturingcost of the optical system can be reduced and a miniaturized opticalisolator can be realized.

While the present invention has been described and illustrated hereinwith reference to the preferred embodiment thereof, it will beunderstood by those skilled in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the invention.

What is claimed is:
 1. An optical isolator comprising:a plurality ofoptical fibers for transmitting light beams; a pair of collimatinglenses for converting said light beams emitted from or entered into saidoptical fibers into parallel light beams; a pair of symmetricbirefringent elements, having at least one tapered surface, for emittingby polarization said plurality of parallel light beams having passedsaid collimating lenses, and condensing all said light beams travelingin a forward direction onto said optical fibers, respectively; and aFaraday rotator, interposed between said birefringent elements, forrotating said light beams incident thereto by 45°.
 2. An opticalisolator as claimed in claim 1, wherein each of said birefringentelements has a plurality of tapered faces which have a plurality oftapered angles, respectively, and which are formed on one surface ofsaid birefringent element.
 3. An optical isolator as claimed in claim 2,wherein said tapered faces of said birefringent elements have the sametapered angle.
 4. An optical isolator as claimed in claim 2, whereinsaid tapered faces of said birefringent elements are arranged to facesaid pair of collimating lenses, respectively.
 5. An optical isolator asclaimed in claim 1, wherein each of said birefringent elements has acrystal axis having an angle of 45° clockwise or counterclockwise.